There is strong experimental and theoretical evidence that structural discontinuity and the material orthotropy that results from it affect the 3D spread of electrical activity in the heart. This behaviour should be accounted for accurately in cardiac activation models. However, in order to do so, it is necessary to incorporate 3D structural detail at a scale that imposes considerable computational overheads. As a result, the use of detailed, tissue-specific 3D models can prove to be intractable in studies of reentrant arrhythmia where it is necessary to model repeated cycles of electrical activation. Alternative approaches here include the development of realistic higher order descriptions of 3D electrical properties or the use of 2D models that capture key features of 3D structure and electrical behaviour. The use of these approaches to investigate the contributions of structural discontinuity to normal electrical propagation and to reentrant activation in the right atrium and in the border zone surrounding a myocardial infarct will be outlined. The extent to which structural discontinuities provides a substrate for inactivation across the excitable gap when defibrillation strength shocks are applied during reentrant arrhythmia will also be considered.

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